Inshore/Offshore Gradients of Imposex in Bolinus Brandaris (Gastropoda: Muricidae) from the Gulf of Gabès (Southern Tunisia, Central Mediterranean Sea)
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ISSn: 0001-5113 - AAdrAY ACTA AdrIAT., 54(2): 299 - 314, 2013 Inshore/offshore gradients of imposex in Bolinus brandaris (Gastropoda: Muricidae) from the Gulf of Gabès (southern Tunisia, Central Mediterranean Sea) Kamel Elhasni1*, Paulo VasconcElos2,3, Mohamed GhorbEl1 and othman Jarboui1 1 Institut National des Sciences et Technologies de la Mer (INSTM), Centre de Sfax, B.P. 1035, Sfax 3018, Tunisie 2 Instituto Português do Mar e da Atmosfera (I.P./IPMA), Avenida 5 de Outubro s/n, P-8700-305 Olhão, Portugal 3 Centro de Estudos do Ambiente e do Mar (CESAM), Departamento de Biologia, Universidade de Aveiro, Campus de Santiago, P-3810-193 Aveiro, Portugal *Corresponding author, e-mail: [email protected] The present study provides the first data available on imposex in a gastropod species caught offshore the Tunisian coast. Imposex was analysed in the purple dye murex (bolinus brandaris) from ten collecting sites offshore the Gulf of Gabès (southern Tunisia, Central Mediterranean Sea). From a total of 584 individuals analysed, females outnumbered males, leading to a female-biased sex ratio (1 F:0.7 M). Among the 353 females analysed, 117 were affected by imposex. On the whole, these females presented low to moderate imposex incidence (I%=33.1) and severity (FPLI=0.3, RPLI=2.6 and VDSI=0.8). The study revealed that imposex is a widespread phenomenon in the Gulf of Gabès and identified a clear inshore/offshore gradient in the imposex indices of b. brandaris. Regression analysis detected highly significant negative correlations between imposex indices and the distance to the coastline and depth of the collecting sites. Principal components analysis highlighted the specific influence of the distance to the major harbours, either in number of calling vessels (commercial harbour of Sfax) or shipping tonnage (oil terminal of Skhira). This inshore/offshore gradient of imposex development in b. brandaris reflects marked spatial variation in pollution by organotin compounds associated to the shipping activity. Overall, the study provides valuable baseline data for assessing the future evolution of imposex in b. brandaris, and subsequently the spatial and temporal trends of pollution by organotin compounds offshore the Gulf of Gabès. Key words: Bolinus brandaris, imposex, pollution biomonitoring, inshore/offshore gradient, Gulf of Gabès, southern Tunisia InTroduCTIon tion that induces imposex has been causally associated to pollution by organotin compounds imposex is a masculinisation phenomenon (tributyltin - TbT and triphenyltin - TPT), which that consists of the development and superim- were used worldwide as biocides in antifouling position of male secondary sexual characters paints applied on ships and boats hulls (TEr- (penis and/or vas deferens) onto females of lizzi et al., 2001). because of this ubiquitous prosobranch gastropods. The endocrine disrup- environmental contamination, imposex became 300 ACTA ADriaTica, 54(2): 299 - 314, 2013 a widespread phenomenon, affecting an increas- 2009a, 2011, 2012; lahbib et al., 2011a), and more ing number of both coastal and offshore gastro- recently Conus mediterraneus, Cyclope neritea, pods (Ellis & PaTTisina, 1990; horiGuchi et al., Nassarius mutabilis, Nassarius nitidus and Stra- 2000; sTErnbErG et al., 2010). indeed, nowadays monita haemastoma have also been studied for imposex is reported to affect more than 260 spe- imposex in Tunisia (lahbib et al., 2010, 2011a). cies worldwide, distributed among 33 families Typically, imposex monitoring is performed and largely dominated by species belonging to in coastal areas, particularly in the vicinities of family Muricidae (100 species) (TiTlEY-o’nEal commercial harbours, fishing ports, shipyards et al., 2011). and marinas, in order to detect point sources The purple dye murex, Bolinus brandaris (hotspots) of contamination by organotin com- (linnaeus, 1758), is a common muricid gastro- pounds. in contrast, studies in offshore areas pod found along the entire Mediterranean sea, are much scarcer, but allowed confirming the while in the atlantic ocean its occurrence is widespread character of the imposex phenom- mainly restricted to the Portuguese and Moroc- enon (Ellis & PaTTisina, 1990), affecting gastro- can coasts (PoPPE & GoTo, 1991; houarT, 2001). pod species even in presumably more pristine imposex in B. brandaris has been monitored in regions (e.g. sTranD et al., 2006, 2009). similarly, several locations throughout its distributional in the Gulf of Gabès (southern Tunisia), impo- range, especially in the northern Mediterranean, sex has been monitored in H. trunculus collected firstly in spain (Morcillo & PorTE, 1998, 1999; in coastal waters (TriGui El MEnif et al., 2007; solé et al., 1998; raMón & aMor, 2001, 2002; Tira- lahbib et al., 2007, 2008a, 2009a), but there are no Do & salas, 2001) and then in italy (chiaVarini studies on imposex in gastropod species caught et al., 2003). along the southern Mediterranean, in offshore areas. imposex studies with B. brandaris are scarcer The purple dye murex (B. brandaris) is and limited to Moroccan (lEMGhich & bEna- among several gastropod species caught as by- Jiba, 2007) and Tunisian coasts, namely in the catch by bottom trawling in the Gulf of Gabès. Gulf of Tunis and in the bizerte lagoon (abiDli recent surveys in this area showed that B. et al., 2009a, 2011, 2012; lahbib et al., 2011a). in the brandaris is distributed mainly in the 10−80 m atlantic ocean, the only information available depth range, with highest by-catches per unit on imposex in B. brandaris was obtained off effort (bcPuE = total biomass hour-1) occur- southern spain (GóMEz-ariza et al., 2006) and ring between 40 and 60 m depth (K. Elhasni, along southern Portugal (lanGsTon et al., 1997; unpublished data). These catches provide an excel- coElho, 2005; VasconcElos et al., 2010, 2011). lent opportunity for assessing the incidence and Tunisia has an impressing coastline of 1300 severity of imposex in B. brandaris, as well as km bordered by the central Mediterranean sea. their spatial and depth distribution in offshore since the last decade there has been a remark- areas of the Gulf of Gabès. To the author’s best able effort in monitoring imposex and its effects knowledge, this study reports the first data avail- in some gastropod species distributed along the able on imposex in a gastropod species caught Tunisian coasts, with particular emphasis on offshore the Tunisian coast. sites with intense shipping activity and conse- quent organotin pollution. in Tunisian waters, MaterIAl And MeThodS imposex was firstly described in Hexaplex trun- culus by lahbib et al. (2004) and since then this Study area and collecting sites species has been subject of numerous studies in this country (TriGui El MEnif et al., 2006, 2007; The Gulf of Gabès is situated in southeastern abiDli et al., 2007, 2009a,b, 2012; lahbib et al., Tunisia (southern ionian sea, approximately 2007, 2008a,b, 2009a,b, 2010, 2011a,b). as mentioned between 33 and 35ºn), spreading from cap above, other gastropod species monitored for Kapoudia in the north to the libyan border in imposex include B. brandaris (abiDli et al., the south (fig. 1). The gulf opens eastwards to Elhasni et al.: inshore/offshore gradients of imposex in Bolinus brandaris... 301 Fig. 1. Map showing the study area offshore the Gulf of Gabès (southern Tunisia, Central Mediterranean Sea) and the collecting sites surveyed for analysing imposex in bolinus brandaris the offshore and comprises some large islands harbour is sfax (1608 ships), followed by zarzis (Kerkennah and Djerba) and coastal lagoons (1009 ships) and Gabès (720 ships). however, (bougrara and El bibane). This area corre- in terms of total cargo tonnage, the oil terminal sponds roughly to 58% of the Tunisian coastline, of skhira assumes prevalence (5402 thousand comprising a wide continental shelf with soft tonnes), followed by the commercial harbours slope, characterised by shallow bottoms and of sfax (5145 thousand tonnes) and Gabès (4261 weak currents. The Gulf of Gabès has an intense thousand tonnes) (Table 1). tidal regime compared to other Mediterranean The Gulf of Gabès is the most important areas, with semidiurnal tides and a mean tidal fishing area in Tunisia. in the last decade range reaching 1.6 m (sErbaJi, 2000). (2000-2009), this area contributed for 34 to The study area is characterised by an intense 49% (mean≈43%) of the country annual fishery shipping activity associated to the main com- production, although with decreasing landings mercial harbours in the Gulf of Gabès (from in recent years (DGPa, 2009). Therefore, the study north to south: sfax, skhira, Gabès and zarzis) area is also subjected to a significant boating (fig. 1). according to official data (oMMP, 2007), activity connected to the main fishing ports in 2007 these harbours received 43.9% of the (from north to south: sfax, Mahrès, skhira, ships calling Tunisian harbours and represented Gabès and zarzis) in the Gulf of Gabès (fig. 52.6% of the national cargo tonnage (Table 1). 1). The typology of the fishing fleet includes in terms of shipping traffic, the most important from small boats operating inshore to large 302 ACTA ADriaTica, 54(2): 299 - 314, 2013 Table 1. Number of calling vessels and shipping tonnage in the main harbours of the Gulf of Gabès during 2007 (Data source: OMMP, 2007) Calling vessels Shipping tonnage harbour number Gulf of Gabès (%) Tunisia (%) Tonnes (1000) Gulf of Gabès (%) Tunisia (%) sfax 1608 45.1 19.8 5145 33.2 17.4 zarzis 1009 28.3 12.4 704 4.5 2.4 Gabès 720 20.2 8.9 4261 27.5 14.4 skhira 226 6.3 2.8 5402 34.8 18.3 Total 3563 100.0 43.9 15512 100.0 52.6 bottom trawlers operating offshore. The most cision 0.05 mm). The shell of B. brandaris is important fishing port is also sfax, harbouring quite fragile and frequently damaged by bottom a high number of small boats and around 270 trawling (particularly in the siphonal canal).